Armature Voltage Calculator for DC Motor
Easily calculate armature voltage for DC motors using speed, torque, current, and resistance. Includes formulas, examples, and a step-by-step guide.
torque and armature voltage relation
The armature (terminal) voltage of a DC motor can be computed by: V a = E b + I a R a. Calculate back-EMF Eb at speed: E b = k e o, being able to find its speed (omega) = rad/s or E b = (k e n) at speed = rpm, depending on your constant. Assuming that torque and motor constant are known, obtain I a = T / k t and then V a = E b + (T/k t) R a.
Formula & Table Summary:
- Armature (terminal) voltage: Va = Eb + Ia·Ra
- Back EMF (constant flux): Eb = ke · ω (V, ω in rad/s) or Eb = ke_r · n (n in rpm)
- Torque ↔ Current (constant flux): T = kt · Ia → Ia = T / kt
- Speed conversion: ω (rad/s) = 2π·n / 60
Converter: Input → Output
| Input available | Use / Formula | Output |
|---|---|---|
| Speed (n rpm), motor constant ke_r, Ia, Ra | Eb=ke_r·n → Va=Eb+Ia·Ra | Armature voltage Va (V) |
| Torque T, kt, speed (n) and Ra | Ia=T/kt; Eb=ke_r·n; Va=Eb+Ia·Ra | Va (V) |
| Measured Va, Ia, Ra | Eb=Va−Ia·Ra; speed from Eb/ke | Back EMF Eb and speed |
dc motor resistance calculator
Armature voltage to a DC motor is the terminal voltage Which is applied between the armature winding that develops the needed armature current and back EMF. In the case of a simple DC motor: V a = E b + I a R a, V a is armature (terminal) voltage, E b is back EMF (inversely proportional to speed and flux), I a is armature current and R a is armature resistance. Back EMF may be given as Eb = ke x Ph w (or Eb = ke x w ) and torque as T = kt x Ph x Ia (or T = kt x Ia x). This manual provides the basic equations, a table of input/output converters, and some sample calculations to calculate armature voltage using speed, torque, current, resistance, or motor constants.
dc motor efficiency calculator
| Scenario | Input | Calculation | Result |
|---|---|---|---|
| Given speed & current | n = 1500 rpm, ke_r=0.04 V/rpm, Ia=10 A, Ra=0.5 Ω | Eb=0.04×1500=60 V; Va=60+10×0.5 | Va=65.0 V |
| Given torque & speed | T=20 N·m, kt=0.5 N·m/A, n=1000 rpm, ke_r=0.05 V/rpm, Ra=0.2 Ω | Ia=20/0.5=40 A; Eb=0.05×1000=50 V; Va=50+40×0.2 | Va=58.0 V |
| Back-calc speed | Measured Va=220 V, Ia=5 A, Ra=1 Ω, ke_r=0.1 V/rpm | Eb=220−5×1=215 V; n=Eb/ke_r | n=215 / 0.1 = 2150 rpm |
| Low-current small motor | n=3000 rpm, ke_r=0.02 V/rpm, Ia=0.5 A, Ra=2 Ω | Eb=0.02×3000=60 V; Va=60+0.5×2 | Va=61.0 V |
Frequently Asked Questions - Armature Voltage Calculator for DC Motor:
What is armature voltage in a DC motor?
It is the voltage applied to the motor’s armature winding, equal to back EMF plus armature current times resistance.
How do you calculate armature voltage?
Use Va = Eb + Ia·Ra, where Eb is back EMF, Ia is armature current, and Ra is armature resistance.
What is back EMF in a DC motor?
Back EMF is the voltage generated by the motor’s rotation that opposes the applied armature voltage.
How do you calculate back EMF?
Eb = ke·ω or Eb = ke_r·n, where ke is motor constant, ω is angular speed, and n is rpm.
What is the relation between torque and current?
Torque T = kt·Ia, so armature current Ia = T / kt when flux is constant.
What happens if armature resistance is high?
Higher Ra increases voltage drop (Ia·Ra), reducing motor efficiency and speed.
Can you find speed from armature voltage?
Yes, Eb = Va − Ia·Ra; then speed n = Eb / ke_r.
Why is armature voltage important?
It controls the motor speed and performance by balancing back EMF and resistive drop.
What units are used for armature voltage?
Armature voltage is measured in volts (V).
Is armature voltage the same as supply voltage?
Not always, because supply voltage equals back EMF plus the Ia·Ra voltage drop.
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